An acorn is a seed which will grow into an oak tree once planted. Players must have at least level 15 Farming to plant it. Once grown, the resulting tree may be cut down using a hatchet to grant Woodcutting experience points and to gather oak logs. If a player does not dig up the stump, the tree will regrow. To dig up a stump, use a spade on it. Digging up the stump will yield oak roots and the tree patch will be cleared for growing another tree.

Acorns can be a surprising source of wealth, due to the oak roots resulting from digging up the tree. Unlike other common tree roots, which are usually dropped at first opportunity, oak roots can be used in brewing. If done correctly, players could make 43,667 coins per root if they manage to brew a keg of axeman's folly (m) at current prices.

The oak tree will take 160 minutes (4 x 40 minutes) to become fully grown, depending on whether or not the tree becomes diseased in the process of growing. Even if a farmer is paid to watch a tree, it may still become diseased. The farmer will immediately cure the tree, but the tree will take longer to grow.